Sound transmitter and receiver



H. C. HAYES SOUND TRANSMITTER AND RECEIVER I Fe 3. 1925.

Filed July 7, 1923 FIG. 2.

FIG. 1

NIH

Z s we M MH 0 u a H Patented Feb. 3,1925.

UNITED STAT S PATENT" OFFICE.

HARVEY o. HAYES, or wasnmeron, nis'rrucr or COLUMBIA.

scum) TRANSMITTER AND RECEIVER.

. Application filed July 7,

ments in Sound Transmitters and Receivers,

of which the following is a specification.

. My invention relates broadly to devices for converting soundvibrations into electrlcal vibrations or transferring recelvedelectrical vibrations into sound vibrations,

and more particularly to a construction of sound transmitter orreproducer with oper ating qualities of great eiiiciency' and designedto eliminate distortion inherent in apparatus heretofore available. Oneof the objects of my invention isto provide a construction of magneticsound device which may be employed either as a transmitter or receiverat will and which substantially eliminates distortion of sound.

Another object of the invention is to provide an arrangement ofvibrating parts for a sound receiver or transmitter wherein the magneticdriving forces corresponding to the electrical vibrations employed aresubjected to a considerable distributed area of the vibrating partsintegrating the driving forces throughout an extended area to convertthe electrical vibrations into sound vibrations of relatively largeamplitude.

Another object of the invention is to provide a plurality of cooperatingmagnets assembled in a transmitter or reproducer construction wherebyrelatively large driving forces may be imparted to the mechanicallymoving parts to secure relatively large amplitude vibration bydifferential action of the magnets one upon the other. Another object ofthe invention is to provide a construction. of sound transmltter whereinan amplification of theelectrical vibrations produced by sound waves maybe secured within the circuits associated with the transmitter.

A further object of the invention is to provide a practical constructionof sound reproducer and transmitter having many advantageswhich 'will bepointed out hereinafter, and which construction is capable ofmanufacture and assembly at reasonable cost on a quantity productionbasis.

M stood invention w1ll be more clearly underdrawings, in which:

by reference to the accompanying Figure 1 is a side elevation of my as-1923. Serial No. 650,184.

sembled sound transmitter and reproducer; Fig. 2 is a cross-sectionalview of the sound transmitter and reproducer illustrated in Fig. 1; F1g.3 is a plan view of the apparatus as illustrated in Fig. 1 looking inthe direction of the terminals and adjusting means forming a part of theapparatus;

Fig. 4 is a cross-sectional view taken on line 44 of Fig. 2 illustratingthe construction of the mechanically moving arts of my apparatus; andFig. 5 is a schematic wiring diagram illustratin the circuits employedin my apparatuslw ereby it may function either as a transmitter orreceiver.

Heretofore in the art practically all dev1ces for transmitting andreceiving sound have been either very insensitive or else they havedistorted and destroyed the true quality of the sound in such a way asto make the reproduction unfaithful and unsatisfactory. .Distortion ofthe sound, both by the transmitter and receiver, is in a large measuredue to resonance of the vibrating s stem, which usually consists of adia- The usual method for overcoming this difiiculty is to design theapparatus such that the vibrating parts are resonant at frequencies wellabove the sound range through which the apparatus will operate inpractice. This requires that a slight displacement of the moving systemmust bring a large restoring force into play, and under such conditionsthe device becomesvery insensitive, especially when the design is suchthat the restoring forces brought into play are due to stiffness of thedistorted member or members for then the mass which is required of suchmembers gives so much inertia that it is diflicult to impose forcedvibrations on the movable system. Large restoring forces can be broughtinto play by using light dia- Y hragms or other members under tension utsuch arrangements are unsatisfactory for various reasons.

My invention involves a different method for overcoming the resonancedefects inherent in sound receiving and transmitting apparatusheretofore available, consisting broadly in making the moving parts solight that they'are readily forced into vibration and with so littlerestoring force that the fundamental resonance frequency is below theoperatin range of sounds and the harmonics can damped out. There are anumber of factors to be overcome in apply- 7 struction which will besensitive over a wide range of frequencies, including among others thefollowing:

(a) Since the restoring forces brought intoplay through a. displacementof the movable members is very slight, these members must be'balancedand their motion produced by reciprocating forces;

(1)) Since the moving members are very light and bring but smallrestoring forces into play when they are distorted, the members will notmove as a whole but will tend to. vibrate only over a region surroundingthe point or points where the reciprocating forces are applied. Undersuch conditions the device can neither radiate or absorb much soundenergy and will therefore be inetlicient;

() In many cases the electrical imped- -ance of such devices needs to beseveral thousand ohms, and therefore, in order tha; the resistancelosses should not be high it is necessary to use fairly large coils; v(cl) In case of all receivers of the loud speaker class the electricalinput must be amplified greatly, and this requires the use ofcomplicatedand expensive auxiliary apparatus.

The construction shown in the accompanying drawings overcomes thefactors listed above, as will be hereinafter described.

4 I provide a casing represented by refer v ence character 1 forming aprotectlve housing for the apparatus with an annular screw threaded ring2 at one end and an inwardly turned flange 3 atthe other end, betweenwhich the magnetic and mechanical parts of my apparatus are secured. Tworing shaped magnets 4 and 5 are fit-ted'together by an annular joint 6forming an annular rim supporting a light unstretched diapiiragm 7 whichserves as the movalble memr. This diaphragm is coned except for a smallportion of its center at 8 and an annular port-ion about the outer areaat 9. This design makes the diaphragm rigid even though it isconstructedof thin material and confines its deflection to the annularportion 9. The diaphragm 7 is generally made of non-metallic materialand, if made of such material, carries on opposite sides two similarlight weight annular rings 10 and 11 of magnetic material, or othersuitable construction to provide for magnetic act-ion between the.diaphragm and the magnets. These magnetic rings 10 and 11 are solocated with respect to the diaphragm 7 that they bridge the annularpole faces 12 and 13 i of magnet 5, and 14 and 15 of magnet 4, leaving asmall equal air space between each ring and its respective pole pieces.Insulate ed annular rings 23 and 24; bridge the gaps between the polefaces 12 and 13 and 14 and 15 respectively B reason of the symmetry ofthe design, the diaphragm is attracted toward each magnet 4c and 5 withequal force, provided the two magnets are of equal strength andtherefore the diaphragm is balanced.

It will be noted that the driving force is applied over an extendedcircular area and not at a point in the center of the diaphragm as hasheretofore been the practice. The flexible portion 9 of the diaphragmand position of the driving forces revents distorting the diaphragm atthe point where the force is applied and thereby tends to prevent theformation of harmonics. Thetwo magnets 4 and 5 are permanentlymagnetized with their like poles opposing, that is, the inside pole ofeach magnet and the outside pole of each magnet are alike as topolarity. Two separate windings are carried upon each magnet, onewinding connecting with the sending or receiving circuit, depending uponwhether the apparatus is used for a transmitter or receiver, and theother of which may be left open-circuited or connected through a localmicrophone circuit for amplifying the telephonic signals. The separatewindings on magnet ,4 are indicated at 16 and 17, and the windings onmagnet 5 are shown at 18 and19.

As will be more clearly seen in Fig. 5, the magnet coils 16 and 18 areconnected in series, but in such a sense that the current in coil 18strengthens or weakens its magnet 5 at the same time that the current incoil 16 weakens or strengthens its magnet 4 respectively. In otherwords, these two coils 16 and 18 form a differential winding on thedevice as a whole. This differential principle of winding causes thediaphragm armatures 10 and 11 to be driven back and forth between thepole faces 12, 13, 14 and 15 whenever an alternating current passesthrough the two coils 16 and 18, since it causes a variation in themagnetic flux linkage betweenthe armature and the two magnets,increasing the linkage with one magnet and at the same time decreasingthe linkage with the other, and vice versa, as the current alternates.The magnet windings 16 and 18 This apparatus as described functions as Ian excellent telephone receiver or as a loud speaker without distortionof the reproduced sound. When coils 19 and 17 are used by connection toterminals26 and 27 the device may serve both as a loud speaker and atransmitter. Coils 1'9 and 17 are wound in the same sense as are coils18 and 16 re spectively, and are connected in series phra m '7.

through a microphone 25, one electrode of which is formed by, or oerated by, the d1a- The micro one 25 is mounted on adjusting rod 28 wich passes through bushing 29 wherein it may be acted upon by set screw30 to fix the microphone in the best operating position with relation todiaphragm 7 The object of this arrangement is to increase, or amplify,the driving force on the diaphragm 7. This is accomplished as follows:Any motion of the diaphragm, whether produced by the voice or othersource of sound meeting the diaphragm or by a telephonic currenttraversing the telephone coils, causes the current in the microphonencircuit to vary as a result' of a change in the electrical resistancethrough the microphone. The sense of the current through the microphonecoils 19 and 17 is made such that any variation in this current broughtabout by motion of the diaphragm will be such as to amplify thediaphragm movement. In this way the diaphragm can be subjected to largeaccelerating forces, as is required of a loud speakin telephone, and itcan be caused to move agamst high damping as is required of anon-resonant transmitter.

While I have described my invention in a certain specific embodiment itis to be understood that various changes may be made within the scope ofthe appended claims without departing from the spirit of the invention.I have found that the device 0porates well if the movable microphoneelectrode is separated from the diaphragm by an air space, thus causingthe electrode to be moved by the change in pressure of the interveningair caused by motion of the diaphragm. It is also evident that themethod of linking a microphone with a diaphragm in such a way as toutilize the variation of the microphonic current for amplifying themotion of the diaphragm, which is causing the variation, can be appliedto other than the balanced diaphragm.

Having thus described my invention, what I claim and desire to secure byLetters Patent of the United States is as follows 1. An apparatus forconverting electrical vibrations into sound vibrations, comprising incombination a pair of annular magnets positioned adjacent each other, asetof annular pole pieces on each of said magnets, a diaphragmpositioned between said ma nets, and a magnetic annular ring carried byand movable with said diaphragm in a position adjacent said pole faces.

2. An apparatus for converting electrical vibrations into soundvibrations, comprim'ng-in combination a pair of annular .magnets locatedadjacent each other, annular. pole faces carried by eachof said magnets,a diaphragm positioned between said magnets, magnetic annular rincarried on. said diaphragm adjacent sai pole faces,

-and a conical portion in the center of said diaphragm.

3. An apparatus for converting electrical vibrations into soundvibrations, comprising in combination an annular magnet, a pair ofannular pole faces carried by said magnet, and a diaphragm mountedadjacent said magnet havin a magnetic annular ring carried on" saidiaphragm and adjacent said pole faces and a conical portion in thecenter of said diaphragm."

4. An apparatus for converting electrical vibrations into soundvibrations,,comprising in combination an annular magnet, a

pair of annular pole pieces carried by said magnet, a diaphragm mountedadjacent said magnet, said diaphragm comprising a conical portionadjacent the center thereof and a flexible horizontal portion adjacentthe outer edge thereof, and a magnetic ring carried by said diaphragm ina position intermediate said conical and flexible portions adjacent saidpole faces.

5. An apparatus for convertingelectrical vibrations into soundvibrations, comprising in combination a pair of annular mag netic framemembers fitting one within the other, a pair of annular pole facescarried by eachof said magnetic frame members, a balanced diaphragmpositioned between said magnetic frame members, said diaphragm having aconical portion adjacent its center. and a flexible portion adjacent itsouter edge and fiat magnetic annular rings carried on each side of saiddiaphragm in a position intermediate said conical portion and saidflexible portion, and windings carried on said magnetic frame membersfor energizing said magnets in accordance with electrical vibrationswhereby said diaphragm functions to convert said electrical vibrationsinto soundvibrations.

6. In an apparatus for transmitting and receiving electrical vibrations,the combination of a pair of annular magnetic frames fitting one withinthe other, a pair of anprising in combination a pair of annular magneticframes, a diaphragm mounted between said frames, said diaphragmcomprising a conical portion adjacent its center and a horizontalflexible portion adjacent its outer edge, a pair of magnetic annularrings mounted on opposite sides of said diaphragm in a positionintermediate said conical portion and said outer flexible portion, amicrophone operatively connected with the center of said diaphragm, aplurality of magnet windings on said frames, said windings beingconnected in series with said,

microphone whereby sound vibrations directed against said diaphragmcause corresponding current variations through said magnet, windings andsaid microphone.

8. In a transmitter for sound vibrations, the combination of an annularmagnet frame, a pair of annular pole faces carried by said frame, adiaphragm mounted adjacent said frame, said diaphragm having a conicalportion adjacent its center and a.

horizontal flexible portion adjacent its outer edge, a magnetic annularring carried by said diaphragm in a position intermediate said conicalportion and said flexible portion, a microphone connected with thecenter of said diaphragm, and a plurality of magnet windings carried bysaid magnet frame and electrically connected in series with saidmicrophone.

9. An apparatus for converting electrical vibrations into soundvibrations, comprising in combination a pair of annular magnets locatedadjacent each other, annular'pole pieces carried by each ofsaid'magnets, a non-metallic diaphragm positioned between said magnets,a magnetic ring carried on the flexible portion of said diaphragmadapted to be acted upon by the pole pieces of the magnets.

HARVEY C. HAYES.

